Machine tools generally are made in small size and lower cost, and can be coupled with different application tools to form a wide variety of styles, such as grinding discs, emery wheel machines, drilling machines, electric wrenches and the like, to assist operators to quickly perform certain tasks, thus are popularly accepted on the market. Besides electric power tools driven by electric power, there are also pneumatic tools driven by pressurized air.
However, when a machine tool is operating, dust is easily generated and could affect workpieces or cleanness of environments. Hence most machine tools now on the market are equipped with a dust suction device to clean the dust generated during operation. For instance, R.O.C. patent No. M245007 discloses an air exhaust apparatus for pneumatic grinders. It mainly includes a body with an upper extension and a lower extension extended from the circumference of the body and formed in a juxtaposed fashion. The upper extension has an air intake vent connected to an air intake duct. The lower extension has a dust hood at a lower side that has an opening to hold a grinding disc. The grinding disc has dust suction apertures. The lower extension further has a dust collection duct at a lateral side connected to a dust collection bag. When the air intake duct introduces air to drive the grinder to operate, the dust generated during grinding of the grinding disc is introduced through the dust suction apertures and passes through the dust hood to enter the lower extension of the body, and then is further directed through the dust collection duct to enter the dust collection bag coupled on a distal end of the dust collection duct.
R.O.C. patent No. 517618 also discloses an air exhaust apparatus for pneumatic grinders. It includes a grinding wheel with dust suction apertures formed thereon and a dust-proof cover located at the upper end of the grinding wheel. The dust-proof cover is fastened to a motor casing which has a chamber to hold an air motor set with movable vanes. The motor casing has an air intake duct and an air discharge duct extended from one side thereof and formed integrally. The air intake duct and air discharge duct hold respectively an air intake valve set and an air discharge muffler set, and also form a housing chamber to hold a throttle valve and a regulation knob, two opposing wings extended from the top surface thereof and formed integrally, and a movable air intake trigger located thereon. The dust-proof cover contains a holding trough extended therefrom and pivotably connected to an air exhaust duct of the motor casing. The holding trough is extended to a duct junction of the dust-proof cover. The air exhaust duct of the motor casing has an L-shaped tube with a lower end coupled with a flow guiding plate so that airflow generated by the movable vanes of the air motor set is discharged upwards through an air outlet. The tube has a lower end extended close to a front end of an outlet of the duct junction of the dust-proof cover so that the exhaust air of the motor and the outlet of the duct junction of the dust-proof cover form a converged location where the dust can be rapidly sucked and removed due to the powerful exhaust airflow during grinding. The regulation knob is held at a junction of the air exhaust duct and the air discharge duct, and has a carved portion and a wall to control the selection of an air exhaust path through the air exhaust duct or the air discharge duct.
All the aforesaid conventional techniques of the machine tools clean dust by installing a dust collection duct at one side of the machine tool to suck the dust during operation of the machine tool. The dust collection duct can only clean part of the dust at certain positions, especially at the operating position. Furthermore, the conventional machine tool has an installation hole on the handgrip to install a pressing switch which is depressed to activate operation of the machine tool. As dust generated everywhere during operation of the machine tool, it easily enters the machine tool through gaps formed between the pressing switch and installation hole, and even invade the interior of the cylinder that is rotated at a high speed to cause damage of the internal elements of the machine tool.